Patent Literature 1 discloses a device using a reflective spatial light modulator (SLM). In the device disclosed in the literature, two mirrors are arranged on a virtual reference straight line, while a reflective SLM is disposed at a position vertically shifted from the virtual reference straight line. Input light entering along the virtual reference straight line is reflected by one of the mirrors, so as to impinge on the SLM. This light is modulated by the SLM, reflected by the other mirror, and then outputted along the virtual reference straight line.
Techniques for applying the SLM to laser processing devices, microscopes, and the like have recently been under study. In the case where the SLM is applied to a laser processing device, for example, phase-modulating a laser beam with a phase-modulating SLM and converging the phase-modulated laser beam at a processing site through a light collecting lens can compensate for the aberration at the converging point, thereby enhancing the processing accuracy.
In the case where the SLM is applied to a microscope, a subject site must be observed while being illuminated with light. In the case where the SLM is applied to a processing device, it is also desirable for the subject site (processing site) to be observable in order to specify the processing position with a high accuracy. Therefore, in general, the subject site is irradiated with illumination light having a wavelength different from that of the laser beam, and the reflected light or scattered light (hereinafter referred to as observation light) generated at the subject site upon irradiation with the illumination light is received, so as to observe the site.